1. Field of the Invention
The present invention relates to a failure diagnosis system for automobile engines which is used in a vehicle production process when performing a performance test on an engine before the same is assembled onto a vehicle body. Particularly, the invention concerns an equipment for determining the goodness or badness of the engine according to the sound or vibration thereof.
2. Description of the Related Art
A known failure diagnosis system for automobile engines has been disclosed in, for example, Japanese Patent Application Laid-Open Publication No. Hei 4-242138.
In this known failure diagnosis system for automobile engines, determination of whether the engine is good or bad is made by actually driving the engine before the same is assembled onto the vehicle body, namely by supplying water, fuel and electricity to the engine and thereby actually performing the engine operation by firing. The determination (evaluation) of a failure of the engine sound in this failure diagnosis system for automobile engines is made by maintaining the rotations number of the engine operated by firing to be fixed, extracting the sound of the engine by a microphone, frequency analyzing the engine sound extracted by the microphone, and detecting the frequency of the engine sound that exceeds a threshold value.
However, in the method of determining a failure of the engine by actually firing-operating the above-described known engine, since actual abnormal sounds of the engine are hidden by the suction sound and exhaust sound (combination sound) as well as the noises of the factories near the engine and the noises such as the another-engine operation sound, ventilation equipment sound (fan rotation sound, air blowing sound, etc.), etc. there is the problem that difficulties arise in automatically extracting characteristics of the engine sound through frequency analyses and quantifying it. Also, since the firing-operation of the engine is impossible to execute unless the assembly thereof is complete, there is the problem that many steps and a significantly large amount of time are needed for repairing the engine after abnormalities have been found out.